This feels like a dumb question, but I'll shoot anyways...

For a stock L98 engine, how hot should the exhaust manifolds generally be at operating temperature?

I'm thinking that there's no good "general" answer to the question, as a lot of different properties could affect the temps. I'm just curious as to what, if anything, one could infer from knowing what the surface temperatures of different points of the exhaust manifolds are.

I just recently purchased an infared thermometer (up to 600 deg F) from Fry's with the intention of measuring the exhaust temperatures--just to see how consistient the numbers would be going across each manifold. I let the engine run for about 10 minutes then tested, and I noticed a couple of things.

First of all, the manifolds were about 40 deg F hotter in the middle of the manifolds as opposed to the sides. I suppose that could just be because the two inside ports are closer together. Also, I noticed that the passenger side was about 60+ deg F hotter than the driver's at many points. I'm not sure if I should be worried about that or not--I'm wondering if it could just be that there's a lot more crap on that side of the engine (i.e. A/C, emissions).

Of course, mabye I'm underestimating the exhaust temperatures in the first place and my meter won't even go that high... (in which case, I'll probably return it)

 

this may seem dumb too....

but did you measure the temperature with car off? because if so, the manifolds may cool in a different pattern...

if that's the case, measure the temperature with the car on

just out of curiosity (I posted this before), how hot do the manifolds get? 600 F?

 

Yes, the engine was running and the coolant temperature was at 220 deg F (it had been sitting for an hour or so, so it was still warm when it was started).

As far as how hot manifolds generally get: that's what I want to know.

 

I'm not sure how hot the exterior surfaces of the manifolds might get, but the exhaust gasses are about 1,800°F. The cat converter has to maintain 1,600°F just to be effective. Although the manifolds will shed some heat to the surrounding air and heads, I'd guess they easily exceed 600°F, and are likely closer to 900°F or higher at peak operating conditions. I know that aluminum won't last around exhaust manifolds, and it melts at right around 1,100°F.